RCU Forums - Dale's Nitro Mill Rebuild Guide (new or used) Parts I,II

Dale's Nitro Mill Rebuild Guide (new or used)

PART I - Crankcase

I have been rebuilding and resealing engines for years now. I have found that by doing it the right way that engines run much more consistent then they did before I started doing this. With this method, the engines are super easy to tune, start easier, hold a more consistent tune, idle forever without stalling and last longer. I wanted to share this with everyone. Many of you probably do this already. For those that don't follow along and you might learn something.

This process is easy. There are a few things that can ruin engines from doing this process. This includes going too fast, being careless and not having the right tools. Otherwise, you will be fine. If you are convinced that you cannot do this, then you probably shouldn't. You will probably ruin your mill. You will be better off to run an engine until it dies and take it to a hobby shop to replace/repair.

If you are unsure but confident that you can do this then you can. Let's move along. Before you pull that new engine out of the box, bolt a clutch too it and slap it on the engine mounts, reconsider first. Your engine was built in high volume in a large factory overseas. The only one that cares about your engine lasting and running optimally is you. Manufacturing folks do the best they can, but they can overlook thing and make mistakes.

If your engine was built on the 12th hour of an employees 12 hour shift on Friday night, it might not be as carefully assembled then if it was built on the 2nd hour on Monday morning after a restful weekend. Quality processes are supposed to catch defects, but they aren't 100% processes. You might be surprised at what you find when you open the brand new engine- you might find loose screws, small pieces of metal or dirt, torn o-rings or even preexisting damage. It is worth the few hours for you to pull the new mill apart and rebuild it.

First, carefully pull the mill apart and put all of the parts on a paper towel or on a table. Inspect all of the parts for any damage. Look at the sleeve and piston for any deep scratches.

http://www.intergate.com/~rpurcell/r...ect/giga24.JPG

Next, clean the crankcase. I usually dip the crankcase in denatured alcohol (available at Home Depot in the paint section). I then blow the whole crankcase with compressed air and make sure that it is completely cleaned. When it is clean and dry, then I soak the bearings with a bearing oil (look for something with a long neck to get the front bearing from the back). When the bearings are soaked, I use my finger to work the bearings back and forth and make sure the oil penetrates the bearings sufficiently. Then I wipe the excess oil off of the exterior part of the front bearing so it doesn't attract dirt.

Crankcase is ready, or in my case crankcases (My dual giga crusher project)

http://www.intergate.com/~rpurcell/r...ect/axial1.jpg

Next, I dip the crankshaft into the alcohol and blow it dry with a compressor. I then generously apply after run oil to the portions of the crankshaft that roll on the crank bearings and then insert the crank into the case.

http://www.intergate.com/~rpurcell/r...ect/axial2.jpg

http://www.intergate.com/~rpurcell/r...ect/axial3.jpg

Next, dip the piston/conrod unit into the alcohol and blow it dry with a compressor. Do not wipe the piston dry. A paper towel might scratch the piston. Next, generously apply after run oil to the wrist pin and con rod. I really douse this one. This is probably one of the hardest working junctions in a nitro engine.

http://www.intergate.com/~rpurcell/r...ect/axial4.jpg

Then very carefully guide the piston into the crankcase. Do not let the piston grind against the side of the crankcase on it's way down. ALSO!!! Important! Most pistons have a cutout on one side to clear the crankshaft. If you install the piston incorrectly, it will hit the crankcase and go 'boom'! Carefully guide the connecting rod over the crankshaft and slide the conrod onto the crankshaft. Generously apply oil to this junction.

http://www.intergate.com/~rpurcell/r...ect/axial5.jpg

Next, dip the sleeve into the alcohol and blow it dry. Again, do not wipe the sleeve. Allow it to air dry. Then apply after run oil to the bottom of the sleeve where it will first make contact with the piston. Then carefully guide the sleeve into the crankcase and align it with the piston so the piston slides right up into the sleeve. I usually apply a few drops of oil to the top of the piston and then push the sleeve in all of the way. Make sure the sleeve aligns properly with the crankcase (usually a little indent or pin for alignment).

http://www.intergate.com/~rpurcell/r...ect/axial6.jpg

Next, clean the glow plug button surfaces and check the condition of the shims (if any). If the shims are trashed, spend the $2 and replace them. If the shims have a dimple on them from the crankcase, make sure you match the dimple back up when you put the cooling head back on.

It is common to have some gunk in the glow plug threads, so really clean those out. Clean the cooling head mounting surface too. You really want to get a good solid cooling head/button/crankcase mount or you will lose compression. After everything is cleaned, set the glow plug button onto the top of the crankcase and set the cooling head down (On some engines the cooling head and the glow plug button are integrated). Now begin to tighten the cooling head screws evenly in an X pattern. The screws use the cooling head for tension so you don't need threadlock on these screws.

When all of the screws are equally snug, then go through in the X pattern and tighten down the screws. The screws doesn't have to be super tight. It has to be tight, but too tight and you are breaking a cooling head screw. Basically, the cooling head screws distribute the load of the cooling head onto the engine evenly, so overtightening doesn't buy you anything and can break stuff. As a rule, if your allen wrench begins to twist while tightening, that is more then tight enough.

Also, I have a picture of the glow plug I will be using. Make sure you use the glow plug that the engine manufacturer recommends. They have done a lot more research then you as to what range plug works well.

Here is an illustration on the tightening X pattern.

http://www.intergate.com/~rpurcell/r...ect/axial7.jpg

Next, it's time to seal the backplate. I use Permatex black gasket maker RTV. Blue is sufficient too. This stuff is available at any auto parts store. One tube will last you a very long time. I use a toothpick and put an even bead on the back of the crankcase as shown below. Use some alcohol and make sure the crankcase surface is very clean.

http://www.intergate.com/~rpurcell/r...ect/axial8.jpg

Next, I carefully put the backplate on (don't forget to put the pull/roto starter stuff in before you put the backplate on!). I very loosely put the rear screws in after threadlocking them. You don't want to tighten the backplate down or it will squish all of the RTV out and you might as well not even have bothered. You just want the backplate to be 'resting' on the crankcase. Then you want it to cure before you tighten it. Plan on setting the seal and then waiting 24 hours before you fully tighten the backplate screws.

http://www.intergate.com/~rpurcell/r...ect/axial9.jpg

After the sealer dries and you tighten the backplate screws, bolt the pull starter or roto/spin start on. Don't forget to threadlock the starter screws or you will guaranteed lose them. Now, the crankcase portion is done and now you want to seal the carb. Stay tuned for part 2 of this writeup to go over that.

Part 2

Now it's time to get the carb sealed up. If your carb is dirty, then you need to pull it apart and clean it before doing this. If you have a new engine, then you can get started. The first step is to take the high speed needle and components off of the carb housing as shown here. This is typical- you have the needle assembly, a banjo fitting and then 2 washers, one above the banjo fitting and one below the banjo fitting.

http://www.intergate.com/~rpurcell/r...ct/axial13.JPG

Next, clean the surface of everything with denatured or even isopropyl alcohol. Just use a paper tower and make sure all of the surfaces are clean and free of grease or oil. Then, apply a small amount of rtv around the threads of the carb base as shown here.

http://www.intergate.com/~rpurcell/r...ct/axial14.JPG

Then, lightly place the first washer on the RTV. The washers have different internal diameters. Make sure you put the same washer in the location it was in during disassembly.

http://www.intergate.com/~rpurcell/r...ct/axial15.JPG

Next, lightly coat the top and bottom mounting surfaces of the banjo fitting. Don't get carried away. Use a toothpick and put a light bead around the surfaces. If you get carried away, you can get RTV in the fuel inlet and make things worse then when you started!

http://www.intergate.com/~rpurcell/r...ct/axial16.JPG

Next,lightly coat the top of the needle assembly where the washer will mount on and plop the upper washer on.

http://www.intergate.com/~rpurcell/r...ct/axial17.JPG

Then go ahead and carefully put the needle assembly back together. Just lightly thread the assembly, don't fully tighten it down. It is VERY important to get the fuel inlet facing where you need it to face. When you tighten the assembly down, you don't want to twist the banjo anymore or it will mess up the RTV seal. So carefully set the banjo fitting in the right direction as shown below. Finally, tighten the needle down. The banjo fitting will want to move on you, so you will have to hold it in place when tightening. In this case I don't let the RTV set like the backplate because in this case, I am just trying to fill in any gaps between the needle parts.

http://www.intergate.com/~rpurcell/r...ct/axial18.JPG

Finally, put a light bead of rtv around the base of the carb as shown and then plop the carb down onto the crankcase and snug the carb's pinch bolt down.

http://www.intergate.com/~rpurcell/r...ct/axial19.JPG

Here is the installed shot. Note the fuel inlets are in the ideal location and the carb body has been rotated in the crankcase so the linkage is straight.

http://www.intergate.com/~rpurcell/r...ect/giga26.JPG

That's it. Your engine is sealed and ready for action. You will be rewarded for your efforts and be very pleased with the extra preparation you did to the engine. You will notice that the engine doesn't seem as finicky and also that you aren't tweaking the needles as much.

Good luck!